Belt having transverse rigidity

ABSTRACT

A belt with transverse rigidity is constructed so as to prevent the formation of cracks on the surface layer. Belt includes two pairs of sub-layers which provide transverse rigidity. The layers are staggered with respect to one another in order to allow the belt to be driven by a relatively small diameter drum.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a belt having transverse rigidity.

2. Description of the Prior Art

A belt of this type having transverse rigidity is disclosed in EuropeanPatent 0 273 478. In the case of said belt, the layers providingtransverse rigidity comprise a number of cables of, for example, fourwires each having a diameter of 0.6 mm and a spacing of 2.5 mm, locatedsome distance apart in the horizontal plane. Belts of this type havingtransverse rigidity are used, for example, as moving pavements in, forexample, airports or exhibition areas. The layers providing transverserigidity are made of a high modulus material, for example a materialhaving a modulus greater than 50 Giga Pascal. Examples thereof are steelwire and aramide threads. This is in contrast to polyester filaments,nylon threads or other relatively weak materials. One example of a highmodulus material is Fleximat®, which is marketed by the Bekeart Company.A significant advantage of belts of this type compared with aluminiumconstructions composed of a large number of parts is the lowermaintenance and the lower noise level. A problem, which exists with allinstallations, is the diameter of the drum around which the belt, or thealuminium pallet system, has to be guided at the end. If this drum isrelatively large, this means that the floor of a building in which aninstallation of this type has to be installed has to be raised orlowered in order to be able to accommodate the installation and theassociated parts.

In this context a particular advantage of the belt system compared withthe aluminium pallet system is the very small diameter of the drum whichcan be used.

Long-term trials with drums having an even smaller diameter have shownthat no problems occur in the short term but in the long term the outersurfaces of the belt which are subjected to the greatest deformationstress display cracking. Although such cracking has no significanteffect on the mechanical characteristics of the belt and the latter canstill be used for many years without any problems, a psychologicalproblem with regard to the reliability of the belt certainly arises whensaid belts are used for transporting people. The aim of the presentinvention is to prevent said cracking in a belt having transverserigidity.

SUMMARY OF THE INVENTION

This aim is achieved in the case of a belt having transverse rigidity,described above.

The invention is based on the insight that initiation of the cracks doesnot occur at the surface but at the wires which form the layers havingtransverse rigidity. Once the cracks have been initiated there, they arepropagated in the direction of the surface of the belt. On the basis ofthis insight, in contrast to what would appear to be obvious, no attempthas been made to take measures to maintain the surface of the beltundamaged for a longer period, but measures have been taken to preventinitiation of the crack at the cables or wires. If there is noinitiation at the cables, the surface of the belt will likewise notcrack, so that special measures at the surface are not necessary.

Once the insight had been gained that the cracks start at the cables,the following step was to take measures in order to reduce the tensionat the location of the cables. An obvious solution would be simply toincrease the distance between the steel cables. However, this gives riseto the problem that the transverse rigidity of the belt concerned isreduced. It would then be possible to use a larger number of wires percable, but this gives rise to problems because the risk that the cableswill work loose from the rubber during operation and come to the surfaceis appreciably increased. The solution proposed according to theinvention, comprising the arranging of at least two layers of cablessome distance apart, makes it possible to increase the spacing betweenthe cables in each layer while still using the same amount of cablematerial in order to provide an adequate transverse rigidity.

It is pointed out that U.S. Pat. No. 2,850,420 discloses a belt whichhas a so-called `breaker` layer, comprising two sub-layers some distanceapart which provide transverse strength. Here, however, there is noquestion of high modulus material, and, therefore, a belt of this typeis unsuitable for use for the transport of, for example, people becausethis belt will display appreciable sag. Moreover, this belt does nothave a single layer providing longitudinal strength but a pack oflayers, each of which is able to absorb part of a force acting in thelongitudinal direction. Moreover, one of the sub-layers which providestransverse rigidity is arranged directly adjacent to such a layerabsorbing longitudinal stresses.

Consequently, a belt of this type does not have the desired flexiblecharacteristics necessary for its movement over a drum of relativelysmall diameter, which was precisely what gave rise to the problems onwhich the present invention is based.

It is also pointed out that French Patent 72246 discloses a conveyorbelt in which a layer having transverse rigidity is present. Above thislayer a textile layer is provided to prevent the belt from curlingduring hardening of the rubber material at fabrication of the belt. Thistextile material is, as indicated above, not a high modulus material.Consequently, cracking will still occur in the case of a belt of thistype when the latter is subjected to load, as according to theinvention.

As already indicated above, the consequences of the cracking are mostpronounced at the top of the belt. Therefore, in this case a layerproviding transverse rigidity and composed of at least two sub-layers isarranged at the top of the belt. In order also to prevent problems onthe underside, the lowest layer providing transverse rigidity canlikewise be composed of at least two sub-layers.

As in the cables used in the prior art, the wires of which the cablesare composed can also consist of high modulus material in the case ofthe invention. The distance between the cables is preferably between 2.5and 7.5 mm. As in the prior art the cables can comprise any number ofwires. For optimum adhesion, preference is given to three wires.

The spacing between two adjacent sub-layers must, on the one hand, besufficiently small to be able to maintain the concept of a "boxconstruction" of the belt but, on the other hand, must be sufficientlylarge that the crack initiation, described above, in the cables isprevented. It has been found that these conditions can be met in anoptimum manner if the spacing between the sub-layers is between 1 and 3mm and preferably about 2 mm.

The layer providing longitudinal strength can, as is generally known, bearranged in any position between the two layers providing transverserigidity. However, preference is given to arranging said layerapproximately in the centre of the belt.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained in more detail below with reference toan illustrative embodiment shown in the drawing. In the drawing:

FIG. 1 shows a partially exposed perspective view of the belt accordingto the invention;

FIG. 2 shows a cross-section along the line II--II in FIG. 1 and

FIG. 3 shows, in detail, a longitudinal section along the line III--IIIof one of the layers providing transverse rigidity.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIG. 1 the belt according to the invention is indicated in itsentirety by 1. As can also be seen from FIG. 2, said belt comprises arubber support material 2, which extends over the entire height of thebelt. At the top, said rubber material is constructed as a ribbedprofile 8. The following layers are arranged in said rubber support,working from top to bottom:

two sub-layers 3 and 4, which together form the uppermost layer havingtransverse rigidity. In this illustrative embodiment, said sub-layersare approximately 2 mm apart. The distance between the uppermost part ofthe rubber profile 8 and layer 3 is about 8 mm. The distance betweenlayers 4 and 5 is between 6 and 15 mm. The two sub-layers 5 and 6 formthe bottommost layer having transverse rigidity. In this illustrativeembodiment, said sub-layers are approximately 2 mm apart. On theunderside, the belt is bound by 2 mm rubber. Consequently, the belt hasa total thickness which is preferably between 20 and 35 mm.

FIG. 3 shows a longitudinal section of a layer having transverserigidity. It can be seen that said layer is composed of cables 9, whichare located in the layers 3 and 4. The spacing of the cables 9 in alayer is between 2.5 and 7.5 mm and is preferably about 4 mm. Each cable9 is preferably composed of three wires 10 of high modulus material. Thediameter of each wire is about 0.6 mm.

The mechanical characteristics of a layer of this type which hastransverse rigidity and is made up of two sub-layers can be comparedwith a conventional layer having transverse rigidity which is composedof a single layer containing cables having four wires 0.6 mm in diameterand a pitch of 2.5 mm. The amount of steel or other high modulusmaterial incorporated in a layer of this type having transverse rigidityis the same as in the case of the layer having transverse rigidityaccording to the invention, and the strength is therefore the same. Theinvention is based on the insight that by increasing the spacing betweenthe cables the damping and absorbing characteristics of the rubbermaterial can be exploited to an optimum extent and crack initiation isprevented. In the case of the use of three wires, there is optimumadhesion between rubber and cable.

With reference to FIG. 2, a preferred embodiment of the belt accordingto the invention will be described in more detail below.

Example:

In the case of a belt having a total thickness of 30 mm, the height ofthe ribs is 5.0 mm. This is indicated by A. The distance between layer 3and the lower part of the longitudinal ribs is indicated by B and is 3.3mm. With this embodiment, distance C between the two layers 3 and 4 is2.2 mm, whilst layer 7, which provides the longitudinal strength, islocated approximately in the centre of the belt depth, the height oflongitudinal ribs 8 than no longer being taken into account.

With this embodiment, the distance D+E, i.e. the distance between thetwo closest layers providing transverse strength, is 14 mm. The distancebetween the layers 5 and 6, distance F, is 2.2 mm, whilst the distance Gis 2.6 mm.

It can be seen from the above examples that the distance between thelayers 4 and 5 makes up at least 25% of the total belt thickness (inwhich the height of the ribs 8 is not included).

Although the invention has been described above with reference to apreferred embodiment, it must be understood that numerous modificationscan be made thereto without going beyond the scope of the presentinvention. For instance, it is possible to arrange the layer providinglongitudinal strength in a different position, for example adjacent tothe lowermost or uppermost layer providing transverse rigidity.Similarly, the cables can be composed of a number of wires other thanthree and each layer providing transverse rigidity can be composed ofthree or more sub-layers. All such modifications are considered to fallwithin the scope of the appended claims.

I claim:
 1. Belt (1) comprising a rubber support (2) having layers (3-6)embedded in said support and composed of high modulus cables, one ofsaid layers being disposed close to the top and one of said layers beingdisposed close to the bottom of the belt to extend essentiallyperpendicular with respect to the longitudinal axis of the belt over thesubstantially complete belt width to provide transverse rigidity and,between said layers, a single layer (7) extending essentially parallelwith respect to the longitudinal axis of the belt to providelongitudinal strength of the belt, characterized in that at least thelayer located close to the top of the belt, comprises at least twospaced apart sub-layers (3,4) the distance between said sub-layer beingsmaller than the distance from any of said sub-layers to the layerproviding longitudinal strength.
 2. Belt according to claim 1, whereinthe top of the belt is provided with a ribbed profile (8).
 3. Beltaccording to claim 1, wherein the layer provided and located close tothe bottom comprises at least two sub-layers (5, 6) located a smalldistance apart.
 4. Belt according to claim 1, wherein each cable in eachsub-layer comprises approximately three wires (10) of high modulusmaterial.
 5. Belt according to claim 1, wherein each sub-layer iscomposed of a number of cables located some distance apart, the spacingbetween said cables within said sub-layer being between 2.5 and 7.5 mm.6. Belt according to claim 1, wherein the distance between two adjacentsub-layers is between 1 and 3 mm and preferably about 2 mm.
 7. Beltaccording to claim 5, wherein the cables comprising at least one set ofsaid sub-layers are staggered between said sub-layers.